CVE-2020-5136 in SonicOS
Summary
by MITRE • 10/12/2020
A buffer overflow vulnerability in SonicOS allows an authenticated attacker to cause Denial of Service (DoS) in the SSL-VPN and virtual assist portal, which leads to a firewall crash. This vulnerability affected SonicOS Gen 5 version 5.9.1.7, 5.9.1.13, Gen 6 version 6.5.4.7, 6.5.1.12, 6.0.5.3, SonicOSv 6.5.4.v and Gen 7 version 7.0.0.0.
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Analysis
by VulDB Data Team • 11/18/2020
This buffer overflow vulnerability exists within SonicOS firmware versions across multiple generations including Gen 5, Gen 6, and Gen 7, specifically affecting SSL-VPN and virtual assist portal functionalities. The flaw manifests when authenticated attackers exploit improper input validation mechanisms within the SSL-VPN service, allowing them to craft malicious payloads that exceed buffer boundaries and trigger system crashes. The vulnerability represents a critical security weakness that directly impacts the availability and reliability of network infrastructure by enabling remote attackers to perform denial of service attacks against SonicWall firewalls. This issue stems from inadequate bounds checking in the handling of SSL-VPN protocol communications, where user-supplied data is processed without sufficient validation, leading to memory corruption and system instability. The affected versions demonstrate a persistent flaw in the firmware's input processing pipeline that fails to properly sanitize and validate user-provided parameters before they are processed by the SSL-VPN service component.
The technical implementation of this vulnerability involves a classic buffer overflow condition that occurs during the processing of SSL-VPN authentication requests or virtual assist portal communications. When legitimate authenticated users submit specific malformed input data through the SSL-VPN interface, the system's memory management routines fail to properly validate the input size against allocated buffer boundaries. This results in memory corruption that can cause the firewall process to terminate unexpectedly or crash entirely, leading to complete service disruption. The attack vector requires authentication, meaning that only users with valid credentials can exploit this vulnerability, though the impact remains severe as it can effectively disable critical network security services. The vulnerability is particularly concerning because it affects core firewall functionalities that organizations rely upon for network protection and access control. According to CWE classification, this represents a CWE-121: Stack-based Buffer Overflow, which is a well-documented weakness that allows attackers to overwrite adjacent memory locations and potentially execute arbitrary code or cause system crashes.
The operational impact of CVE-2020-5136 extends beyond simple service disruption to encompass broader network security implications that can compromise organizational resilience and business continuity. When the firewall crashes due to this vulnerability, network traffic flows are interrupted, potentially creating security gaps that malicious actors could exploit. Organizations relying on SonicWall firewalls for SSL-VPN access and virtual assist services face significant operational risks, as the system may become unavailable during critical business hours or security incidents. The vulnerability affects multiple firmware versions simultaneously, indicating a systemic flaw that required coordinated patching across different product generations. Network administrators must consider the potential for cascading failures when a firewall becomes unresponsive, as this could impact multiple dependent services and systems that rely on the firewall's availability for proper network operation. This vulnerability also demonstrates how authenticated attacks can be leveraged to create denial of service conditions that are particularly difficult to detect and mitigate in production environments.
Mitigation strategies for this vulnerability require immediate firmware updates from SonicWall to address the buffer overflow conditions in affected versions. Organizations should implement network segmentation and monitoring to detect potential exploitation attempts, as the vulnerability requires authentication to execute successfully. The recommended approach includes applying official patches released by SonicWall that contain fixes for the input validation routines in the SSL-VPN service components. Network administrators should also consider implementing additional access controls and monitoring for SSL-VPN sessions to identify abnormal authentication patterns that might indicate exploitation attempts. According to ATT&CK framework, this vulnerability aligns with T1499.004: Endpoint Denial of Service, which covers techniques that target endpoint devices to cause system unavailability. Organizations should establish incident response procedures that include rapid patch deployment and system recovery protocols to minimize downtime. The vulnerability also highlights the importance of maintaining current firmware versions and implementing proper change management processes to ensure timely security updates are deployed across network infrastructure components. Regular security assessments and vulnerability scanning should be conducted to identify similar buffer overflow conditions that may exist in other network services or applications.